This project is a study of the regulation of expression of genes encoding lens fiber membrane proteins involved in cell-cell communication. We have cloned the gene encoding human major intrinsic protein (MIP) as the first step for studying the regulation of expression of lens membrane genes. MIP, like other members of a putative transmembrane superfamily, contains a 2-fold repeat in its primary structure. This repeat, the NPA box, has been conserved in MIP throughout evolution. The first repeat corresponds to sequences encoded by a single exon; the second corresponds to sequences encoded by three additional exons of the human MIP gene. This raises the possibility that this membrane channel superfamily may have arisen by gene duplication of an ancestor gene. Although 253 bp of the human MIP gene 5' flanking sequence activates expression of the CAT gene in cultured lens epithelia, it does not do so in kidney epithelial cells or NIH-3T3 cells. We obtained several lines of transgenic mice containing as a transgene 253 bp of the human MIP gene 5' flanking sequence fused to the CAT gene. The transgene appears to be preferentially expressed in the lens of one line, while it appears to be specifically expressed in the ovary of another one. We are presently characterizing the cis regulatory elements responsible for activating MIP gene expression in the lens.